This invention relates to an assembly forming a cylindrical cage of spaced apart vanes which is particularly adapted for use in forming guide vanes for use in an air classifier. The classifier may be of the type used for classifying particulate material into a fine fraction and a coarse fraction. The invention is particularly adapted to use with an air classifying device of the type shown in U.S. Pat. No. 4,296,864, issued Oct. 27, 1981.
In air classifying devices of the type to which the present invention relates, there is provided a hollow body having a cage type rotor mounted therein with a motor for rotating the caged rotor. A tangential inlet for classifying air is provided. A plurality of guide vanes are mounted inside of the casing to form a cylindrical cage between the inlet for classifying air and the cage type rotor. These guide vanes serve to direct the classifying air and entrained material into the caged rotor in a tangential direction for classifying particulate material into a fine fraction and a coarse fraction. Details of the operation of the classifier will not be described herein but will be known to those skilled in the art. Other classifiers of this type are illustrated, for example, in U.S. Pat. Nos. 3,669,265; 2,758,713 and 3,015,392.
Common practice prior to the present invention was to utilize separate guide vanes or blades which may be secured as by welding to top and bottom ring members inside the classifier body to form a cylindrical cage. The guide vanes must be appropriately located to perform the dual functions of properly orienting the incoming air flow in a direction tangential to the spinning internal rotor or cage. The second function of the guide vanes is to provide a choked down area or flow path through the area between the guide vanes in order to accelerate the incoming air flow to a desired speed. Since this air flow is usually dust laden with an abrasive material such as ground cement clinker, the guide vanes will wear, necessitating periodic replacement. Since it is desirable to precisely locate the various vanes which make up the assembly, the individual vanes should be placed with a certain degree of precision to assure that the proper spacing and flow path design is achieved. Field replacement of worn vanes in a separator may require arc cutting of the worn vanes and replacement by welding.
In the past, most vanes have been flat metal pieces and in certain instances it would be desirable to shape the vanes in an air-foil shape to improve air flow through the guide vanes to provide for reduced air flow resistance and improve durability and wear resistance of the guide vanes. This could be accomplished by individually casting the guide vanes and then providing a means for positioning the vanes in place.
Since guide vanes are usually welded in place within the classifier, present designs require the use of a material which can be welded. It would be desirable to be able to form the guide vanes out of a wear resistant material which may not be suitable for welding.
U.S. Pat. No. 3,015,392 illustrates an air classifying device with an internal cage type rotor, a tangential classifying air inlet and guide vanes between the air inlet and the rotor. In this patent, the guide vanes have pins at each end which fit into a ring element. This arrangement necessitates the precise location of holes to receive the pins.